1. Field of the Invention
The present invention generally relates to a gas turbine combustor and, more particularly, to an improved cooling structure used in the gas turbine combustor for cooling a combustion liner with a compressed air flowing outside such combustion liner.
2. Description of the Related Art
In the gas turbine engine, in order to improve the turbine efficiency, a tendency is found in recent years to set the temperature of the combustion gas at a turbine inlet to be high. However, increase of the flame temperature tends to result in an increase of the emission of NOx and, therefore, to reduce the emission of NOx, it is necessary to suppress the increase of the flame temperature by increasing the amount of air used for combustion. Accordingly, in order to reduce the air which does not participate in combustion (cooling air), it is desired to increase the convection cooling performance of the combustion liner. The cooling structure for the combustion liner has been well known in the art, in which as shown in FIG. 11, chevron shaped heat transfer enhancement ribs 52 are formed on an outer peripheral surface 51 of the combustion liner 50 in a longitudinal direction L along the direction of flow of a compressed air A from a combustor and also in a transverse direction R along the circumference of the combustion liner 2. (See, for example, the Patent Document 1 listed below.)
The cooling structure has also been well known in the art, in which as shown in FIG. 12, heat transfer enhancement ribs 53 extending straight towards the transverse direction R are formed on the outer peripheral surface 51 of the combustion liner 50 so as to be spaced a predetermined distance from each other. Those known cooling structures are similarly so designed and so configured that, the compressed air A then flowing can collide against the heat transfer enhancement ribs 52 or 53 to form turbulent flows that are utilized to effectively cool the outer surface 51 of the combustion liner 50.
[Patent Document 1] JP Laid-open Patent Publication No. 2006-63984